1. Field of the Invention
The present invention relates generally to instrumentation systems and methods for accessing and preparing treatment sites within the spine (e.g., inter-vertebral motion segments) for subsequent therapeutic procedures, such as, for example, spinal arthroplasty, partial or total disc replacement, annulus repair, vertebroplasty, arthrodesis (fusion), or the like. Disclosed herein are various tools and methods of use (e.g., surgical cutting devices, tissue extractors, etc.) for performing any number of minimally-invasive treatment procedures (e.g., low trauma disc nucleectomy via trans-sacral axial access). The methods can involve, among other things, facilitating the removal of resulting tissue fragments, preparing an intervertebral disc space for subsequent deployment of spinal fusion designed to relieve lower back pain, or motion preservation devices, e.g., dynamic stabilization, devices, prosthetic nucleus devices and total disc replacements designed to relieve lower back pain and to restore physiological function of the lumbar spine, maintain and possibly improve disc health and prevent progression or transition of disease.
2. Description of the Related Art
Chronic lower back pain is a primary cause of lost work days in the United States, and as such is a significant factor affecting both workforce productivity and health care expense. Therapeutic procedures for alleviating back pain range from conservative methods, e.g., with intermittent heat, rest, rehabilitative exercises, and medications to relieve pain, muscle spasm, and inflammation, to progressively more active and invasive surgical means which may be indicated if these treatments are unsuccessful, including various spinal arthroplasties, and eventually even spinal arthrodesis, i.e., surgical fusion.
There are currently over 700,000 surgical procedures performed annually to treat lower back pain in the U.S. In 2004, it is conservatively estimated that there will be more than 200,000 lumbar fusions performed in the U.S., and more than 300,000 worldwide, representing approximately a $1 B endeavor in an attempt to alleviate patients' pain. In addition, statistics show that only about 70% of these procedures performed will be successful in achieving this end.
Moreover, there may be multiple causes for a patient's lower back pain, where the pain generators are hypothesized to comprise one or more of the following: bulging of the posterior annulus or PLL with subsequent nerve impingement; tears, fissures or cracks in the outer, innervated layers of the annulus; motion induced leakage of nuclear material through the annulus and subsequent irritation of surrounding tissue in response to the foreign body reaction, or facet pain. Generally it is believed that 75% of cases are associated with degenerative disc disease, where the intervertebral disc of the spine suffers reduced mechanical functionality due to dehydration of the nucleus pulposus.
The intervertebral discs, located anterior to the vertebral canal, are formed of fibrous cartilage, and comprise the posterior and anterior longitudinal ligaments and the annulus fibrosis, circumferentially enclosing a central mass, the. The nucleus pulposus provides for cushioning and dampening of compressive forces to the spinal column. In a healthy adult spine, it comprises 80% water.
Surgical procedures, such as spinal fusion and discectomy, may alleviate pain, but do not restore normal physiological disc function.
With reference to FIGS. 1A and 1B, the vertebrae are the bony building blocks of the spine. Between each of the vertebral bodies are the spinal discs and this unit, comprising two vertebral bodies interfaced by an intermediate spinal disc, is known as a spinal motion segment. The spine has seven vertebrae in the neck (cervical vertebrae), twelve vertebrae in the mid-back (thoracic vertebrae), and five vertebrae in the low back (lumbar vertebrae). All of the vertebrae and discs are held together or surrounded by means of ligaments, which are strong fibrous soft tissues that firmly attach bones to bones. Ligaments contribute to the normal physiologic range of motion of the spine, and if injured, e.g., due to disc degeneration (described below) and ensuing impact on distribution of physiologic loads, they similarly may contribute to the resulting pain.
Thus, the bony spine is designed so that vertebrae “stacked” together can provide a movable support structure while also protecting the spinal cord's nervous tissue that extends down the spinal column from the brain from injury. Each vertebra has a spinous process, which is a bony prominence behind the spinal cord that shields the cord's nerve tissue. The vertebrae also have a strong bony “body” in front of the spinal cord to provide a platform suitable for weight-bearing.
The spinal discs serve as “dampeners” between each vertebral body that minimize the impact of movement on the spinal column. Each disc is comprised of the nucleus pulposus, a central, softer component, contained with in the, a surrounding outer ring.
With age, the water and protein content of the body's cartilage changes resulting in thinner, more fragile cartilage. Hence, the spinal discs and the facet joints that stack the vertebrae, both of which are partly composed of cartilage, are subject to similar degradation over time. The gradual deterioration of the disc between the vertebrae is known as degenerative disc disease, or spondylosis. Spondylosis is depicted on x-ray tests or MRI scanning of the spine as a narrowing of the normal “disc space” between adjacent vertebrae.
Radiculopathy refers to nerve irritation caused by damage to the disc between the vertebrae. This occurs because of degeneration of the annulus fibrosis of the disc, or due to traumatic injury, or both. Weakening of the annulus may lead to disc bulging and herniation, i.e., the nucleus pulposus or softer portion of the disc can rupture through the annulus and abut the spinal cord or its nerves as they exit the bony spinal column. When disc herniation occurs, the rupture of the nucleus pulposus the annulus fibrosis may irritate adjacent nervous tissue, causing local pain, or discogenic pain, in the affected area. Any level of the spine can be affected by disc degeneration. When disc degeneration affects the spine of the neck, it is referred to as cervical disc disease, while when the mid-back is affected, the condition is referred to as thoracic disc disease. Disc degeneration that affects the lumbar spine causes pain localized to the low back and is sometimes common in older persons and known as lumbago Degenerative arthritis (osteoarthritis) of the facet joints is also a cause of localized lumbar pain that can be diagnosed via x-ray analysis.
The pain from degenerative disc or joint disease of the spine may be treated conservatively with intermittent heat, rest, rehabilitative exercises, and medications to relieve pain, muscle spasm, and inflammation, but if these treatments are unsuccessful, progressively more active interventions may be indicated, including spinal arthroplasty including prosthetic nucleus device implantation; annulus repair, and total disc replacement, and eventually, even spinal arthrodesis, The intervention performed depends on the overall status of the spine, and the age and health of the patient. Procedures include removal of the herniated disc with laminotomy (a small hole in the bone of the spine surrounding the spinal cord), laminectomy (removal of the bony wall), by needle technique through the skin (percutaneous discectomy), disc-dissolving procedures (chemonucleolysis), and others.
When narrowing of the spaces in the spine results in compression of the nerve roots or spinal cord by bony spurs or soft tissues, such as discs, in the spinal canal this condition is known as spinal stenosis. Spinal stenosis occurs most often in the lumbar spine, i.e., the lower back, but also occurs in the cervical spine and less often in the thoracic spine. It is most often caused by degeneration of the discs between the vertebrae due to osteoarthritis. Rheumatoid arthritis usually affects people at an earlier age than osteoarthritis does and is associated with inflammation and enlargement of the soft tissues of the joints. The portions of the vertebral column with the greatest mobility, i.e., the cervical spine, are often the ones most affected in people with rheumatoid arthritis. Non-arthritic causes of spinal stenosis include tumors of the spine, trauma, Paget's disease of bone, and fluorosis.
In the context of the present invention, therapeutic procedures to alleviate pain are restore function are described in a progression of treatment from spinal arthroplasty to spinal arthrodesis. As used herein, spinal arthroplasty encompasses options for treating disc degeneration when arthrodesis is deemed too radical an intervention based on an assessment of the patient's age, degree of disc degeneration, and prognosis.
A wide variety of efforts have been proposed or attempted in the prior art, in an effort to relieve back pain and restore physiological function. Notwithstanding these efforts, there remains a need for methods and tools for accessing and preparing an intervertebral motion segment for subsequent therapeutic procedures, which can be accomplished in a minimally invasive manner.